DbUtils: JDBC Utility Component Examples

DbUtils: JDBC Utility Component Examples

This page provides examples that show how DbUtils may be used.

Basic Usage

DbUtils is a very small library of classes so it won't take long to go through the javadocs for each class. The core classes/interfaces in DbUtils are QueryRunner and ResultSetHandler . You don't need to know about any other DbUtils classes to benefit from using the library. The following example demonstrates how these classes are used together.

// Create a ResultSetHandler implementation to convert the
// first row into an Object[].
ResultSetHandler h = new ResultSetHandler() {
    public Object handle(ResultSet rs) throws SQLException {
        if (!rs.next()) {
            return null;
        }
    
        ResultSetMetaData meta = rs.getMetaData();
        int cols = meta.getColumnCount();
        Object[] result = new Object[cols];

        for (int i = 0; i < cols; i++) {
            result[i] = rs.getObject(i + 1);
        }

        return result;
    }
};

// Create a QueryRunner that will use connections from
// the given DataSource
QueryRunner run = new QueryRunner(dataSource);

// Execute the query and get the results back from the handler
Object[] result = (Object[]) run.query(
    "SELECT * FROM Person WHERE name=?", "John Doe", h);

You could also perform the previous query using a java.sql.Connection object instead of a DataSource. Notice that you are responsible for closing the Connection in this example.

ResultSetHandler h = ... // Define a handler the same as above example

// No DataSource so we must handle Connections manually
QueryRunner run = new QueryRunner();

Connection conn = ... // open a connection
try{
    Object[] result = (Object[]) run.query(
        conn, "SELECT * FROM Person WHERE name=?", "John Doe", h);
	// do something with the result
	
} finally {
    // Use this helper method so we don't have to check for null
    DbUtils.close(conn);  
}

ResultSetHandler Implementations

In the examples above we implemented the ResultSetHandler interface to turn the first row of the ResultSet into an Object[]. This is a fairly generic implementation that can be reused across many projects. In recognition of this DbUtils provides a set of ResultSetHandler implementations in the org.apache.commons.dbutils.handlers package that perform common transformations into arrays, Maps, and JavaBeans. There is a version of each implementation that converts just the first row and another that converts all rows in the ResultSet.

QueryRunner run = new QueryRunner(dataSource);

// Use the BeanHandler implementation to convert the first
// ResultSet row into a Person JavaBean.
ResultSetHandler h = new BeanHandler(Person.class);

// Execute the SQL statement with one replacement parameter and
// return the results in a new Person object generated by the BeanHandler.
Person p = (Person) run.query(
    "SELECT * FROM Person WHERE name=?", "John Doe", h); 

Custom RowProcessor

Each of the provided ResultSetHandler implementations accept a RowProcessor to do the actual conversion of rows into objects. By default the handlers use the BasicRowProcessor implementation but you can implement a custom version to plug in. Probably the most common customization is to implement the toBean() method to handle custom database datatype issues.

Custom BeanProcessor

BasicRowProcessor uses a BeanProcessor to convert ResultSet columns into JavaBean properties. You can subclass and override processing steps to handle datatype mapping specific to your application. The provided implementation delegates datatype conversion to the JDBC driver.

BeanProcessor maps columns to bean properties as documented in the BeanProcessor.toBean() javadoc. Column names must match the bean's property names case insensitively. For example, the firstname column would be stored in the bean by calling its setFirstName() method. However, many database column names include characters that either can't be used or are not typically used in Java method names. You can do one of the following to map these columns to bean properties:

1. Alias the column names in the SQL so they match the Java names: select social_sec# as socialSecurityNumber from person
2. Subclass BeanProcessor and override the mapColumnsToProperties() method to strip out the offending characters.